Solid-state Polycondensation of Other Polyesters

The basic knowledge of the principles of SSP usually allows a generalization concerning the production of any kind of semicrystalline polyester or co-polyester. Differences regarding the reactivities are observed which are attributed to the mobilities of the components employed, e.g. PEN, cationic dyeable polymers or flame-retardant co-polyesters. 

The processing of these prepolymers differs due to the prolonged reaction times during melt-phase polycondensation and the reduced thermal stabilities of these materials. The relatively low IV values of the prepolymers has to be increased by SSP under gentle conditions with the requirement for extremely long reaction times. 

300 °C. This IV region is too low for subsequent PEN processing. Therefore, SSP of the prepolymer is necessary to achieve the desired IV. A sufficiently high IV ( 1.0 g/dl) can be obtained at reasonable but prolonged reaction times via SSP, which is conducted under similar reaction conditions as PET. The reaction is commonly conducted batchwise in vacuo due to the limited commercial demand. 

The SSP of PEN and co-polyesters based on 2,6-naphthalene dicarboxylic acid requires prolonged reaction times, which is obviously related to the rigidity of the monomers and therefore to both the reduced mobilities of the end groups and diffusion. Only a few detailed reports exist in the literature on this subject [31, 32], It should be noted that the analysis of PEN can become complicated due to its reduced solubility. 

An additional example of applying SSP to co-polyester production has been outlined in a US patent [59], This discloses the production of co-polyesters based on terephthalic acid and with up to 12% bis-(hydroxy ethoxy phenyl)sulfone co-monomer content. Additional patents exist concerning the SSP of other copolyesters [60, 61]. 

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